Process of making semiconductors



Oct. 1, 1963 B. ToPAs PROCESS OF MAKING SEMICONDUCTORS Filed Dec. 23, 1960 INVENTOR BENJAMIN TOPAS ATTORNEY United States Patent 3,105,784 PRGCESS OF MAKING SEMICONDUCTORS Benjamin Topas, Snnbury, Pa, assignor to Merck & (30., Inc, Railway, N.J., a corporation of N ew Jersey Filed Dec. 23, 1960, Ser. No. 78,176 1 Claim. (Cl. 156-17) This invention relates to single crystal growth from the vapor phase and, more particularly, it relates to the preparation of improved single crystal substrates for use in such a process.

The process of growth of semiconductor junction devices from the vapor phase, as it is generally recognized today, involves first providing a single crystal substrate or core member of a suitable semiconductor material having a predetermined conductivity type and degree and thereafter depositing onto said substrate from the vapor phase a layer of single crystal semiconductor material, generally of opposite conductivity type and degree from that of said substrate material. In such a process it is highly desirable that growth of said overlayer of semiconductor material assume the same single crystal structure as that of the substrate. However, considerable experimentation has demonstrated that such preferred growth is dependent upon a number of parameters including the degree of crystalline perfection of the substrate crystal, the order of crystalline plane which is exposed to the vapor and, in some instances, the degree of orientation of the plane. Still another critical parameter for oriented growth is the kind of etching pretreatment which is afforded the substrate or core material. While it is generally recognized that etched cores produce better oligo crystals than unetched cores, the proper technique of etching for vapor growth of oriented single crystals is largely unknown.

Accordingly, it is an object of the present invention to provide a method of growing single crystals of a high degree of crystalline perfection from the vapor phase.

Still another object of the present invention is to provide a method of preparing improved single crystal semiconductor substrate members which are particularly adapted to receive single crystal growth thereon.

-A further object of this invention is to provide an etching technique for single crystal semiconductor materials used as substrates in a process of growth of semiconductor junction devices from the vapor phase which is particularly suitable for reception of oriented single crystal growth.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention which will be made with reference to the following drawings.

The FIGURE illustrates in highly schematic form a suitable apparatus for carrying out the method of the present invention.

What has been discovered herein is a method of preparing single crystal semiconductor material used as substrates in the growth of semiconductor junction devices from the vapor phase. In particular, the method of the present invention involves a prescribed pretreatment of said single crystals prior to their being used in such a vapor growth process. Under the conditions described herein, the substrate crystals are subjected to a series of conventional etching procedures, the crystal being protected from the exposure to the adverse effects of air at each stage in the etching procedure.

Referring now to the figure, there is shown a suitable apparatus for carrying out the method of the present invention. The apparatus includes a quartz tube 1 equipped with three stopcocks 2, 3 and 4. Stopcock 2 3,165,784 Patented Oct. 1, 1963 serves as a means of introducing an etching solution 5 which performs a desired etching effect upon the single conductor material 6, such as silicon, having a desired crystalline orientation, is provided within the etching tube. One or more of such crystals may be placed within the tube. Thereafter, the 'cores are subjected to the action of a series of etching solutions, during which time the cores are preferably kept submerged in the solution. At the conclusion of the etching cycle, the cores are rinsed with distilled water. Finally the liquid is displaced by a quantity of argon gas. The cores are then dried under gentle heat afforded by the heating coils and al lowed to dry in the argon atmosphere.

The following will illustrate a specific preferred series of etching solutions, although it will be understood that others known in the art may be used as well. According to this preferred treatment, the cores are first treated with isopropyl alcohol, heated for about five minutes and the alcohol displaced with distilled water and then with argon. A concentrated nitric acid solution followed by an etching solution consisting of 3.7:1 mixture of concentrated nitric acid-hydrofluoric acid is then applied, whereupon the cores are etched in the latter solution for about one and one-half minutes. The etching solution is displaced thereupon with an additional cc. of nitric acid, nitric acid displaced by distilled water while ensuring that the cores are submerged and the cores are rinsed with portions of distilled water. Finally, the distilled water is displaced by argon and the cores are dried in the latter atmosphere.

At the conclusion of the etching cycle described above, the cores are ready to be transferred to a vapor growth reactor chamber. core surfaces have been prepared in a proper manner, the cores will provide the proper nucleation site for growth of oriented single crystals. ly necessary, at this point, it is desirable that the cores be transferred to the reaction chamber under a slight positive flow of inert argon gas.

A particular advantage of the method of the present invention involving pretreatment of single crystal core material is that the desired single crystal growth may be achieved directly by growth from the vapor phase without further treatment of the crystals thus formed. In particular, it is observed that the use of single crystal substrates prepared as described herein completely eliminates the need, as in the past, for zone refining of the deposited crystals thus formed in order to produce well oriented single crystals.

What has been described herein is an etching technique for pretreating single crystal substrate bodies used in a vapor growth process of deposition of semiconductor junction devices wherein single crystal growth of a high degree of crystalline perfection is achieved. In a suitable apparatus the cores are subjected to the action of a series of etching solutions while they are protected from the atmosphere after each successive etching is applied. Thereafter the cores are stored in an inert atmosphere prior to use. In a preferred embodiment, the cores are transferred to the reaction chamber under such an inert atmosphere.

While in this condition wherein the While not absolute While the invention has been particularly shown and described with reference to preferred embodiments thereof, it Will be understood bythose skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

A method of etching a single crystal semiconductor body comprising submerging said body using an etching solution to a level wherein the body is submerged therein, successively displacing said etching solution with a series of other etching solutions thereby protecting the body from exposure to air while said solutions are being til 4 a I applied and finally displacing the solution with an inert gas. a,

References Cited in the file of this patent UNITED STATES PATENTS 

